Numerous species of Mycobacteria exist, some nonpathogenic, some conditionally pathogenic, some inducing an atypical tuberculosis, and some inducing other diseases such as leprosy, arthritis and dermatitis.
These bacteria are complex organisms. M.tuberculosis was thought initially to be composed of 11 major antigens. However, more recent investigation has shown the number of its antigens to be much higher. Some of these antigens are common to several genera, i.e., they show an immunological cross-reactivity between organisms belonging to the super-group Corynebacterium-Mycobacterium-Nocardia. Other antigens are common to all the members of the genus Mycobacterium and a third group of antigens is species-specific.
The interest of investigators in this field was directed toward the mycobacterial species-specific antigens since their use would allow a taxonomic frame for the mycobacteria and also on those antigens whose antigenic power was promising for the elaboration of vaccines.
In 1980, it was recognized (Closs et al (1980): Scand. J. Immunol. 12, 249-263) that M.bovis (attenuated strain BCG) was composed of a large number of antigens revealed through a bidimensional or cross immunoelectrophoresis analyses. These antigens exhibition identifiable precipitation pattern upon such analysis, and these patterns have been assigned a characteristic antigen number. The antigen identified as A 60 was of particular interest in that it was thermostable, a potent immunogen and common --without being identical--to all analyzed Mycobacteria, extending in fact to the whole of the super-group CMN. In particular, A 60 of M.bovis and A 7 of M.leprae were found to be cross-reactive (Harboe et al. (1979) Scand. J. Immunolog. 9, 115-124).